(1) Field of the Invention
This invention relates to power transmission, and more particularly to spring clutches.
(2) Description of the Related Art
Overrunning spring clutches are a well developed art. Such clutches make use of the principle that a spring coil will expand if twisted one way about its axis and contract if twisted the other way. In an exemplary clutch, respective portions of a coil spring are positioned within respective sleeves. In a neutral condition, of the spring portion within each sleeve, an end portion is lightly frictional engaged to the sleeve and a remaining portion is slightly radially spaced from the sleeve. When the sleeves rotate relative to each other about their common axis, friction between the sleeves and the associated end portions will tend to twist the spring. If the relative rotation is in the direction which would tend to contract the spring, there will be slippage or overrunning. If the relative rotation is in the opposite direction, the normal forces between the end portions and sleeve will increase and the heretofore spaced portions will expand into frictional engagement with the sleeves thereby resisting the relative rotation. Accordingly, when such a clutch is used to drive an output from an input rotating (absolutely) in a first direction, the clutch permits the output to rotate faster than the input in the first direction. This permits the output to continue to rotate if the input slows or is stopped. Absolute rotation of the input (or both the input and output) in an opposite second direction may be prevented by additional internal or external mechanisms.
U.S. Pat. No. 5,799,931 (the ""931 patent) discloses an exemplary such spring clutch. In that patent, the spring is formed into a coil by a machining a helical slot in a tubular form (e.g., as distinguished from winding a wire or somehow casting without machining a slot).
One aspect of the invention involves a clutch apparatus having an arbor, a spring, and a sleeve. The arbor has a first end, a second end, and an externally toothed portion. The spring at least partially surrounds the arbor and has an internally toothed portion intermeshed with the arbor externally toothed portion. The sleeve at least partially surrounds the spring and frictionally engages the spring. The engagement is sufficient so that an initial relative rotation between the arbor and sleeve in a first direction tends to uncoil the spring and bias the spring into firmer engagement with the sleeve. The engagement is sufficient that initial relative rotation between the arbor and sleeve in a second direction, opposite the first direction, tends not to uncoil the spring.
In various implementations, a pinion gear may be unitarily formed with the sleeve. The spring may have a slot between interior and exterior surfaces and extending between first and second axial ends and having a nonconstant helix angle. The slot may extend longitudinally at the first axial end and nearly circumferentially at the second axial end.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.